Ha ha ha ha! I gotta tel ya, I was seriously laffin at B&S's reply.
I'm not to sure about file fit rings being better for N02. To tight a fit and the rings will heat up and touch, bind up and cause all soughts of ugly marks on the cylinder wall.
But on the cam, a .500 should fit most any piston. Now, on the piston, what is the number for them.